The present invention relates to antigens from Enterococcus that are useful as vaccines, and to methods for obtaining and using such antigens.
The prevalence of Enterococcus infection is increasing steadily. Strains of Enterococcus now are responsible for 12% of all the nosocomial infections among hospitalized patients and they are the second most common organism isolated from patients with nosocomial infections. This increased prevalence of Enterococcus is due at least in part to the appearance of strains of enterococci that are resistant to antimicrobial agents and therefore difficult to treat with currently available antibiotics. The increase in antibiotic resistance among Enterococcus has increased the importance of alternative prophylactic and therapeutic approaches against enterococcal infections.
Various groups have disclosed polysaccharides isolated from Enterococcus. For example, lipoteichoic acids which contain a 1,3-linked polyglycerophosphate backbone have been isolated from xe2x80x9cS. faecalis,xe2x80x9d which according to current classification is E. faecalis. Position 2 is glycosylated with disaccharides or trisaccharides of glycosyl residues which may be esterified with alanyl residues, and is denoted intracellular teichoic acid because of its predominance between the cell wall and the protoplast membrane. Wicken et al., J. Gen. Microbiol. 33: 231-39 (1963).
Pazur et al., J. Biol. Chem. 246: 1793-98 (1971), have isolated two other polysaccharides from the cell wall of E. faecalis strain N. One of these polysaccharides is characterized as a diheteroglycan consisting of glucose and D-galactose, while the other polysaccharide is said to be a tetraheteroglycan of 2-acetamide-2-deoxy-galactose, galactose, rhamnose, and glucose in molar ratio of 1:1:2:4.
Bleiweis et al., J. Bacterol. 94: 1381-87 (1967), have isolated a third polysaccharide from strain D76 of group D Streptococci. The sugar composition of this material includes glucose, glucosamine, galactosamine, rhamnose, ribitol, and phosphorus; structural information is not provided, however. It is postulated that this material may be ribitol phosphate teichoic acid with attached sugar substituents. It also has been hypothesized that glucose and N-acetyl glucosamine are the possible components of the antigenic site.
Enterococcus antigen(s) capable of eliciting protective antibodies would provide an effective means of preventing and/or treating Enterococcus infection. While the art discloses a variety of Enterococcus antigens, not every antigen is effective as a vaccine. Indeed, none of the material reported in the literature has been shown to be effective in protecting against infection by Enterococcus. In this regard, even a disclosure that an antigen is immunogenic, i.e., that it causes the production of antibodies, provides an insufficient basis for a conclusion that the antibodies are protective and that the antigen therefore is useful in a vaccine.
Finally, the art suggests that Enterococcus serologically is a very diverse genus. This serologic diversity suggested that a vaccine comprised of a practical number of active components was not feasible. Maekawa et al., Microbiol. Immunol. 36: 671-681 (1992).
It is therefore an object of the present invention to provide Enterococcus antigens, particularly antigens from E. faecalis and E. faecium, that are capable of eliciting the production of protective antibodies.
It is a further object to provide a vaccine that contains Enterococcus antigens, more particularly a vaccine that contains antigens from both E. faecalis and E. faecium. 
It is another object to provide a hyperimmune globulin composition that contains antibodies directed against Enterococcus antigens, particularly antigens from E. faecalis and E. faecium. 
In accordance with these and other objects according to the invention, there is provided an isolated Enterococcus antigen that reacts with antibodies to cells from one of ATCC 202013, ATCC 202014, ATCC 202015, ATCC 202016, and ATCC 202017. More particularly, an isolated Enterococcus antigen is selected from the group consisting of an E. faecalis antigen comprising 2-acetamido-2-deoxy-glucose and rhamnose in an approximate 1:2 molar ratio, an E. faecalis antigen comprising a trisaccharide repeat which comprises a 6-deoxy sugar, and an E. faecium antigen comprising 2-acetamido-2-deoxy-galactose and galactose.
The antigen can be used in diagnostic assays or in immunotherapy methods. A conjugate in which the antigen is covalently bonded to an immunocarrier, preferably a recombinantly-produced, non-toxic mutant strain of Pseudomonas aeruginosa exotoxin A or diphtheria toxoid, is provided. The antigen-carrier conjugates are useful in a vaccine, particularly a multivalent vaccine, for active immunotherapy. The antigen or vaccine also can be used to produce immune globulin for passive immunotherapy, or in the production of monoclonal antibodies for diagnostic or therapeutic use.
Other objects, features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.